This invention relates to a system for producing sulfur, and more particularly, to a system for reducing sulfur dioxide by contacting same with coal at elevated temperatures, to produce gaseous elemental sulfur.
Hydrocarbon fuels which are normally burned in industrial installations, such as coal and oil-fired power stations, contain sulfur which, under normal circumstances, is converted to sulfur dioxide in the combustion process. Although in older installations the sulfur dioxide was vented to the atmosphere with the other effluent gases from the process, recent air pollution control requirements have placed great emphasis on removing the sulfur dioxide from the gases before the latter are expelled into the atmosphere. One successful technique in this respect is to remove the sulfur dioxide from polluted gas streams by adsorption on carbon to form sulfuric acid, followed by a regeneration of the adsorbent to produce a stream of high sulfur dioxide concentration.
In order to form a non-polluting by-product that can be accumulated in a useful form, various systems have also been proposed for converting the sulfur dioxide obtained in the foregoing manner to elemental sulfur. However, many of these latter systems require the use of natural gas or some other relatively expensive reducing agent. In this context, U.S. patent application Ser. No. 635,497, filed Nov. 26, 1975 and now U.S. Pat. No. 4,147,762 issued Apr. 3, 1979, by Peter Steiner and assigned to the assignee of the present invention discloses a process in which a gas containing sulfur dioxide is contacted with granular coal to produce sulfur. This has the advantage of utilizing crushed coal, which is the least expensive reducing agent, and is thus very attractive from a cost standpoint.
However, according to this process a less than optimum distribution of the downwardly flowing coal through the vessel as well as the upward flowing sulfur dioxide gas through the coal is achieved. This distribution is particularly important since it is necessary in these type arrangements to achieve the highest efficiency possible.